Coperion GmbH’s twin-screw extruder is being used by Dutch company Dinnissen BV to make, instead of plastics products, a wide range of preserved, wholesome and healthy convenience food.
The key component in this Magi-N.ext line is the ZSK MEGAvolume PLUS twin-screw extruder featuring 54mm diameter screws, which has been custom-made for this application. The starch components of the various recipes are gelatinized by means of an extrusion cooking process. The extruder produces a homogeneous mixture of all the constituents of the recipe and to reduce the moisture entrained by the fresh products such that directly expanded, easily manageable products can be obtained at the pelletizing stage by a centric pelletizer ZGF 70.
According to Coperion, the ZSK MEGAvolume PLUS is equipped with a newly configured process section having an overall length of 10 barrels and featuring two processing zones. The extrusion cooking process takes place in the first zone, while in the second zone the moisture content is reduced with the aid of degassing in conjunction with expansion at the nozzle. Like the entire production line, both the ZSK itself and the downstream ZGF centric pelletizer meet all food processing standards.
The ZSK is first fed with a separately produced premix of the powdered ingredients of the convenience food, e.g. flour from maize, wheat, rye etc. The desired free-flowing fresh food components, such as finely grated carrots or nuts may also be added to this premix. Located immediately downstream of the feed point is a pump for introducing pasty ingredients such as tomato paste or apple sauce directly into the process section.
As said, the shearing action of the twin screws rapidly causes the temperature of the mixture to rise above 100簞C and, in conjunction with the water content of the product, gelatinize the native raw starch. This extrusion cooking process is followed by an intensive degassing process, during which a large proportion of the moisture contained in the product is extracted via a vacuum system. In this section of the extruder, the screw elements ensure optimum surface area exposure of the product and hence efficient degassing.
The product mixture in the extruder is completely compounded by the time it reaches the extrusion die. The compound is extruded into the ZGF centric pelletizer, which in this particular version is equipped with axially movable knife blades, permitting accurate setting of the clearance between the blades and the die plate during operation by means of a scaled adjusting device. The pelletizer produces a directly expanded, easily manageable product that in downstream processes can be further dried, readily coated and enriched with flavorings, vitamins and/or minerals, notes Coperion.